1. Field of the Invention
The present invention is related generally to a method for form ing a component by a subtractive process wherein a porous core is removed for later stage processing. In addition, the present invention is related to such components which find use in semiconductor processing and which require ultra high purity.
2. Description of the Related Art
In the semiconductor industry, device geometries of active components continue to be reduced. Presently, semiconductor devices are being produced having transistor critical dimensions well below one micron, such as less than 0.25 microns. As device geometries continue to shrink, manufacturers of logic as well as memory devices continue to place increasing demands on suppliers of semiconductor process ing equipment to achieve previously unsurpassed purity levels. Semiconductor processing components include components such as wafer paddles, process tubes, wafer boats, liners, pedestals, long boats, cantilever rods, wafer carriers, and vertical process chambers, and the like. Conventionally, such components have been made of fused silica (quartz), which material has served the semiconductor processing community well. However, the desire for improved thermal conductivity and high temperature strength, has spurred development of certain processing components based on other materials, such as silicon carbide.
Conventionally, silicon carbide and siliconized silicon carbide components have relied upon powder processing techniques for fabrication. Use of the powder pathway inherently introduces impurities which are largely unacceptable to the semiconductor processing community. Such impurities typically include iron, aluminum, titanium, vanadium, etc. One conventional technique to address such impurities, is to utilize a high purity CVD coating to seal impurities into the bulk material. However, such a technique has numerous drawbacks. For example, if the CVD coating does not achieve complete coverage, has a defect, or chips or cracks, impurities in the bulk material are free to diffuse into the processing environment, and/or the semiconductor wafers. An example of forming a silicon carbide component by powder processing techniques, followed by silicon impregnation, is shown in U.S. Pat. No. 3,951,587.
To address such drawbacks, formation of highly pure silicon carbide components completely in the gas phase by chemical vapor deposition (CVD) techniques has been investigated. However, such processing is lime consuming, expensive, and limited to simple geometry such as disks, plates and cylinders. Accordingly, standalone CVD silicon carbide components, while achieving desirable impurity levels, are not a viable method for complex shaped silicon carbide components.
Another technique for forming silicon carbide based components involves use of a high purity graphite body, which is converted to silicon carbide by exposure to a silicon containing gas. Background material on this type of processing is described in U.S. Pat. No. 6,162,543. In this technique, a high purity graphite body is exposed to SiO gas under conditions which allow replacement of carbon atoms with silicon atoms to form a stoichiometric beta-silicon carbide body. Generally, such products are then siliconized by impregnation with liquid silicon to form a dense body. While the development of high purity silicon carbide based semiconductor processing components continues to evolve to meet semiconductor manufacturing demands, the need continues to exist in the art for improved semiconductor processing components, and in particular processing technologies for forming such components.